Underwater vehicles equipped with a high-fidelity “synthetic aperture sonar” (SAS) system must have the ability to properly compensate the system's acoustic data in order to determine vehicle motion. To determine vehicle displacements in a direction transverse to a vehicle's trajectory or track, “redundant phase centers” (RPC) are typically used to measure time delays and estimate displacements transverse to the nominal vehicle trajectory. This information is combined with inertial measurement unit data and used to appropriately compensate the acoustic data for transverse deviations and rotations of the vehicle from an ideal track. With respect to the vehicle's “along-track” (AT) motion, it is often assumed that the vehicle can correctly determine its own “speed over the ground” (SOG). If this were the case, the along-track sampling of the synthetic array is uniformly spaced by synchronization of the ping time interval such that the integration of the SOG with time equals a system-designated “advance per ping” (APP). Unfortunately, the underwater environment can affect the vehicle's along-track motion such that the actual APP is different from the system-designated APP. In instances where the SOG is not known to a sufficient accuracy to allow recalculation of the actual APP, the underwater vehicle's actual APP cannot be accurately determined.